Possible Change Default File Association Through Assoc (via process_creation)

title: Possible Change Default File Association Through Assoc (via process_creation)
id: c9dedfdb-5097-5533-8082-4daf5df29b64
status: stable
description: This rule detects file association changes using the builtin "assoc" command. When a file is opened, the default program used to open the file (also called the file association or handler) is checked. File association selections are stored in the Windows Registry and can be edited by users, administrators, or programs that have Registry access or by administrators using the built-in assoc utility. Applications can modify the file association for a given file extension to call an arbitrary program when a file with the given extension is opened.
references:
    - https://attack.mitre.org/techniques/T1546/001/
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1546.001/T1546.001.md
author: Huntrule Team
date: 2026-04-15
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1546.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\cmd.exe'
        - OriginalFileName: 'Cmd.Exe'
    selection_cli:
        CommandLine|contains: 'assoc'
    condition: all of selection_*
falsepositives:
    - Unknown
level: low
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_cmd_assoc_execution/info.yml